Heat developable color light-sensitive materials are known. Heat developable color light-sensitive materials and heat development process are described in Research Disclosure (May, 1978), pp. 54-58 (RD-16966) and U.S. Pat. Nos. 3,985,655, 4,463,079, 4,474,867, 4,478,927, 4,507,380, 4,500,626 and 4,483,914. Among them, dye diffusion transfer type heat developable color light-sensitive materials are preferred wherein a dye providing compound capable of releasing or forming a diffusible dye by heat development is used in combination with silver halide emulsions, and the diffusible dye is transferred to an image receiving element during or after heat development, because a dye image can be obtained in a short period of time and unexposed silver halides and other components can be separated from the dye image.
Laser diodes emitting radiations in the region of near infrared to infrared rays have been developed, and many image forming methods using the same have been proposed with the reduction in the cost of the diodes in recent years. Some of the methods have been put to practical use.
Generally, silver halide emulsions are not sensitive to infrared rays, so when silver halide photographic materials are used in image forming methods using the above-described light source, the silver halide emulsions must be spectrally sensitized by sensitizing dyes.
However, silver halides spectrally sensitized with the sensitizing dyes have a tendency in which the lowering in sensitivity from a wavelength giving the maximum sensitivity to a shorter wavelength is small as the wavelength in the spectral sensitization region becomes longer. This tendency is particularly remarkable with silver halide emulsions spectrally sensitized to the infrared region [for example, see Akira Sasai, Photographic Chemistry, Shashin Kogyo Shuppansha (1982), page 116, FIG. 9.5]. Therefore, in the preparation of infrared-sensitive light-sensitive materials, the problem which needs to be solved is that a light-sensitive layer for longer wavelengths is exposed to a light source for the exposure of a light-sensitive layer for shorter wavelengths, and as a result, a diffusible dye is formed in both layers. Namely, the problem of a lowering in color separation must be solved.
A means for solving this problem is keeping the spectral sensitization wavelength regions of light-sensitive layers having a spectral sensitivity in the infrared region separated from each other. On the other hand, the laser diodes which are frequently used are the laser diodes in the wavelength region of 750 to 850 nm, which are inexpensive and produced in many different types. Although there are laser diodes in the region of longer wavelengths, there is difficulty in conducting spectral sensitization in the region of such longer wavelengths, and problems of low sensitivity and high fog are caused. Accordingly, a method for improving color separation for a difference in wavelength by 100 nm at most is needed.
In color light-sensitive materials having light sensitivity in the visible region, filter layers are commonly used as a means for improving color separation. U.S. Pat. No. 4,619,892 discloses that the filter layer is applied to a color light-sensitive material having light sensitivity in the infrared region. This art discloses a color light-sensitive material wherein a filter layer is provided between a first infrared-sensitive layer and a second infrared-sensitive layer having sensitivity to shorter wavelengths than that of the first layer, the filter layer absorbing infrared rays which overlap with the maximum sensitivity region of the second infrared-sensitive layer without absorbing more than 40% of infrared rays to which the first infrared-sensitive layer is sensitized.
To carry out sufficient color separation with such a filter layer, it is necessary to develop an infrared dye having very sharp spectral characteristics. Further, a dye previously dispersed by emulsification and dispersion or solid dispersion must be prepared. Thus, production costs are greatly increased.
Further, when a reflective support (paper or resin-coated paper) is used as a support, it is necessary that in addition to the infrared dye, an irradiation-preventing dye which absorbs infrared rays to which a light-sensitive layer spectrally sensitized to the infrared region of the longest wavelength is exposed is contained in the light-sensitive layer, or an anti-halation layer containing such a dye is provided under the light-sensitive layer. Accordingly, costs are further increased.